I'm a fan of the AVGN, and also Yahtzee's Zero Punctuation. That's about all I'll watch except some HVGN, if he'd ever start posting videos again. As for the Nostalgia Critic I've watched a couple, but stopped all of a sudden. Don't dislike him, just stopped. Might just have to pick that up again.
I'm going with NC because all his comedy and takes in his reviews are hilarious. Don't get me wrong AVGN is also awesome with his reviews on retro games, but the NC won me over because of his humor and his other characters like TGWTG and Chester A. Bum. My favorite review's so far by him is Mortal Kombat Annihilation, Street Fighter, and Howard the Duck. I also love the AVGN vs NC fights especially the Brawl that was too fucking win.
I love both of them and even though AVGN was the one i discovered first I'll still side with the NC because of his epic jokes and weekly updates.
AVGN is good to but the recent episodes has gone down quite abit on the joke factor but as Klown said I would still watch them even if it just became a pure non-joke / only facts serie.